FieldAwareFactorizationMachines trainer can't have any empty arguments list

[rogancarr]

The FieldAwareFactorizationMachines trainer cannot be given an empty arguments list.

var ffmTrainer = mlContext.BinaryClassification.Trainers.FieldAwareFactorizationMachine(
    new FieldAwareFactorizationMachineBinaryClassificationTrainer.Options { });

or

var ffmTrainer = mlContext.BinaryClassification.Trainers.FieldAwareFactorizationMachine(
    new string[] {"Features"});

I suggest allowing an empty arguments list by default. cc @sfilipi